Complex metal oxide catalyst with high (meth) acrylic acid selectivity

ABSTRACT

Disclosed are a Mo—Bi—Nb—Te based composite metal oxide; and a process for producing (meth)acrylic acid from at least one reaction material selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, wherein the Mo—Bi—Nb—Te based composite metal oxide is used as a catalyst. Also, disclosed is a process for producing (meth)acrylic acid comprising a first step of producing (meth)acrolein as a main product from at least one reaction material selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, and a second step of producing (meth)acrylic acid from the (meth)acrolein, wherein yield of (meth)acrylic acid in the product of the first step is 20 mole % or higher.

This application claims priority to U.S. patent application Ser. No.11/502,027, filed Aug. 10, 2008, which claims the benefit of the filingdate of Korean Patent Application No. 2005-73402, filed on Aug. 10,2005, in the Korean Intellectual Property Office, the disclosure of eachof which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to a Mo—Bi—Nb—Te based composite metaloxide, and a process for producing (meth)acrylic acid from propylene orthe like by using the Mo—Bi—Nb—Te based composite metal oxide as acatalyst. Also, the present invention relates to a process for producing(meth)acrylic acid comprising a first step of producing (meth)acroleinas a main product from propylene or the like, and a second step ofproducing (meth)acrylic acid from the (meth)acrolein, wherein the yieldof (meth)acrylic acid in the product of the first step is 20 mole % orhigher.

BACKGROUND ART

A process for producing an unsaturated fatty acid from an olefin by wayof an unsaturated aldehyde is a typical process of catalytic vapor phaseoxidation. To perform partial oxidation of olefins, composite oxidescontaining molybdenum and bismuth, molybdenum and vanadium, or mixturesthereof are used as catalysts. Particular examples of such catalyticvapor phase oxidation include a process of producing (meth)acrylic acidby the oxidation of propylene or isobutylene by way of (meth)acrolein, aprocess of producing phthalic anhydride by the oxidation of naphthaleneor orthoxylene, and a process of producing maleic anhydride by thepartial oxidation of benzene, butylene or butadiene.

Generally, (meth)acrylic acid, a final product, is produced from atleast one reaction material selected from the group consisting ofpropylene, propane, isobutylene, t-butyl alcohol or methyl-t-butyl ether(referred to as ‘propylene or the like’, hereinafter) by a two-stepprocess of vapor phase catalytic partial oxidation. More particularly,in the first step, propylene or the like is oxidized by oxygen, inertgas for dilution, water steam and a certain amount of a catalyst, so asto produce (meth)acrolein as a main product. Then, in the second step,the (meth)acrolein is oxidized by oxygen, inert gas for dilution, watersteam and a certain amount of a catalyst, so as to produce (meth)acrylicacid. The catalyst used in the first step is a Mo—Bi-based multinarymetal oxide, which oxidizes propylene or the like to produce(meth)acrolein as a main product. Also, some acrolein is continuouslyoxidized on the same catalyst to partially produce (meth)acrylic acid.The catalyst used in the second step is a Mo—V-based multinary metaloxide, which mainly oxidizes (meth)acrolein in the mixed gas containingthe (meth)acrolein produced from the first step to produce (meth)acrylicacid as a main product.

A reactor for performing the aforementioned process is provided eitherin such a manner that both the two-steps can be performed in one system,or in such a manner that the two steps can be performed in differentsystems.

As mentioned hereinbefore, the first-step catalyst involved in vaporphase partial oxidation using propylene or the like as a startingmaterial is a multinary metal oxide, with which (meth)acrolein isproduced as a main product and at most 10% of (meth)acrylic acid isproduced.

As disclosed in Japanese Laid-Open Patent No. Hei8-3093, a conventionalfirst-step catalyst is a composite oxide represented by the formula ofMo_(a)—Bi_(b)—Fe_(c)—A_(d)—B_(e)—C_(f)—D_(g)—O_(x), wherein Mo, Bi andFe represent molybdenum, bismuth and iron, respectively; A is nickeland/or cobalt; B is at least one element selected from the groupconsisting of manganese, zinc, calcium, magnesium, tin and lead; C is atleast one element selected from the group consisting of phosphorus,boron, arsenic, Group 6B elements in the Periodic Table, tungsten,antimony and silicon; D is at least one element selected from the groupconsisting of potassium, rubidium, cesium and thallium; each of a, b, c,e, f and g is a number satisfying the conditions of 0<b≦10, 0<c≦10,1≦d≦10, 0≦e≦10, 0≦f≦20, and 0<g≦2, when a=12; and x is a value definedby the oxidation state of each element. When vapor phase catalyticoxidation of propylene is performed with molecular oxygen by using theabove first-step catalyst and by operating the first-step catalyst layerat a temperature of 325° C., acrolein is produced with a yield of 81.3%and acrylic acid is produced with a yield of 11%. In other words,acrylic acid content is low in the reaction product obtained by usingthe first-step catalyst.

Meanwhile, Japanese Laid-Open Patent No. Hei5-293389 discloses acatalyst represented by the formula ofMo_(a)Bi_(b)Fe_(c)A_(d)X_(e)Y_(f)Z_(g)Si_(h)O_(i), wherein Mo, Bi, Fe,Si and O represent molybdenum, bismuth, iron, silicon and oxygen,respectively; A is at least one element selected from the groupconsisting of cobalt and nickel; X is at least one element selected fromthe group consisting of magnesium, zinc, manganese, calcium, chrome,niobium, silver, barium, tin, tantalum and lead; Y is at least oneelement selected from the group consisting of phosphorus, boron, sulfur,selenium, Group 6B elements in the Periodic Table, cerium, tungsten,antimony and titanium; Z is at least one element selected from the groupconsisting of lithium, sodium, potassium, rubidium, cesium and thallium;and each of a, b, c, d, e, f, g, h and i represents the atomic ratio ofeach element, with the proviso that when a=12, b=0.01˜3, c=0.01˜5,d=1˜12, e=0˜6, f=0˜5, g=0.001˜1, h=0˜20, and i is the oxygen atom numberneeded to satisfy the atomic valence of each element. When vapor phasecatalytic oxidation of propylene is performed by using the abovefirst-step catalyst to produce acrolein and acrylic acid, acrylic acidis produced with a yield of 6.2 mole % under a propylene conversionratio of 99.1 mole % and an acrolein selectivity of 89.6 mole %. Inother words, acrylic acid content is still low in the reaction productobtained by using the first-step catalyst.

In a process for producing (meth)acrylic acid, the temperature of thesecond-step catalyst layer varies depending on the selectivity of(meth)acrolein and (meth)acrylic acid (i.e. the first-step catalyticreaction product) and the amount of (meth)acrolein unreacted in thesecond-step catalytic reaction. The second-step catalyst layer isoperated in such a manner that unreacted (meth)acrolein can beminimized. When (meth)acrolein selectivity is high in the first-stepcatalytic reaction product, the second-step catalyst layer is subjectedto an increased load and concentration, resulting in an increase inreaction temperature and degradation of the lifetime of the catalyst.Additionally, when a concentration of unreacted (meth)acrolein isincreased due to the degradation in catalytic activity, a waste gasincineration system (WGIS) may be overloaded, resulting in degradationof the lifetime of a waste gas treating catalyst.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has been made in view of theabove-mentioned problems. The inventors of the present invention havefound that when a Mo—Bi—Nb—Te based composite metal oxide is used as thefirst-step catalyst in the production of (meth)acrylic acid frompropylene or the like, yield and/or selectivity of (meth)acrylic acidincreases in the first-step reaction product, and thus (meth)acroleinload and concentration decrease in the second-step to such a degree that(meth)acrolein conversion ratio can reach 100%. The present invention isbased on this finding.

According to an aspect of the present invention, there is provided aMo—Bi—Nb—Te based composite metal oxide.

According to another aspect of the present invention, there is provideda process for producing (meth)acrylic acid from at least one reactionmaterial selected from the group consisting of propylene, propane,isobutylene, t-butyl alcohol and methyl-t-butyl ether by using aMo—Bi—Nb—Te based composite metal oxide as a catalyst.

According to still another aspect of the present invention, there isprovided a process for producing (meth)acrylic acid comprising a firststep of producing (meth)acrolein as a main product from at least onereaction material selected from the group consisting of propylene,propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, and asecond step of producing (meth)acrylic acid from the (meth)acrolein,wherein yield of (meth)acrylic acid in the product of the first step is20 mole % or higher.

Hereinafter, the present invention will be explained in more detail.

Mo—Bi-based first-step metal oxide catalysts for producing(meth)acrolein from propylene or the like, which have been disclosed todate, generally provide a conversion ratio (selectivity) from propyleneor the like to (meth)acrolein and (meth)acrylic acid of about 90% ormore, wherein the molar ratio of (meth)acrolein to (meth)acrylic acid inthe first-step reaction product is about 9:1. Additionally, when thefirst-step reaction product is subjected to the second-step reaction, itis possible to obtain a (meth)acrolein conversion ratio of about 98%.

The inventors of the present invention have found that when aMo—Bi-based composite oxide also containing both Nb and Te, i.e. aMo—Bi—Nb—Te based composite metal oxide is prepared and used as thefirst-step reaction catalyst, it is possible to obtain a conversionratio (selectivity) of (meth)acrolein and (meth)acrylic acid frompropylene or the like of 90% or more, as well as a molar ratio of(meth)acrolein to (meth)acrylic acid in the first-step reaction productof approximately 8:2˜7:3.

Additionally, the inventors of the present invention have found that useof a Mo—Bi—Nb—Te based composite metal oxide as the first-step catalystprovides a decreased selectivity of (meth)acrolein in the first-stepreaction product and an increased selectivity of (meth)acrylic acid asmentioned above, and thus the second-step reaction is subjected to adecreased load and concentration of (meth)acrolein as a reactant, sothat the second-step reaction can provide a (meth)acrolein conversionratio of 100% after the completion of the reaction.

Further, according to the present invention, since selectivity of(meth)acrylic acid increases from (meth)acrolein and (meth)acrylic acid,which are the main reaction products that have passed through thefirst-step catalyst, complete conversion of (meth)acrolein can beaccomplished in the subsequent second-step catalytic reaction step.Hence, it is possible to operate the overall process under a high loadand concentration so as to provide a high yield, and to improve thelifetime of the second-step catalyst.

In brief, the present invention is based on the fact that a Mo—Bi—Nb—Tebased composite metal oxide, used as the first-step reaction catalyst ina process for producing (meth)acrylic acid from propylene or the like,provides a lower (meth)acrolein selectivity and a higher (meth)acrylicacid selectivity in the first-step reaction product, when compared toother conventional Mo—Bi metal oxides currently used as the first-stepcatalyst.

(1) Preferably, the Mo—Bi—Nb—Te based composite metal oxide according tothe present invention is a composite metal oxide represented by thefollowing Formula 1:MO_(a) Bi_(b) Nb_(c) Te_(d) A_(e) B_(f) C_(g) D_(h) E_(i) F_(j)O_(k)  [Formula 1]

Wherein Mo represents molybdenum, Bi represents bismuth, Nb representsniobium, and Te represents tellurium;

A is at least one element selected from the group consisting of W, Sb,As, P, Sn and Pb;

B is at least one element selected from the group consisting of Fe, Zn,Cr, Mn, Cu, Ru, Pd, Ag and Ru;

C is at least one element selected from the group consisting of Co, Cd,Ta, Pt and Ni;

D is at least one element selected from the group consisting of Si, Al,Zr, V and Ce;

E is at least one element selected from the group consisting of Se, Ga,Ti, Ge, Rh and Au;

F is at least one element selected from the group consisting of Na, K,Li, Rb, Cs, Ca, Mg, Sr, Ba and MgO;

each of a, b, c, d, e, f, g, h, i, j and k represents the atomic ratioof each element;

wherein when a=12, b is 0.01˜20, c is 0.001˜20, d is 0.001˜20, e is0˜15, f is 0˜20, g is 0˜20, h is 0˜10, i is 0˜10, j is 0˜10, and k is anumber defined by the oxidation state of each of the above elements.

When used as a catalyst, the Mo—Bi—Nb—Te based composite metal oxideaccording to the present invention may be used alone or may be supportedon an inert carrier. Particular examples of the carrier that may be usedin the present invention include porous or non-porous alumina,silica-alumina, silicon carbide, titanium dioxide, magnesium oxide,aluminum sponge, or the like. Additionally, the carrier may take acylindrical shape, a hollow cylindrical shape or a spherical shape, butis not limited thereto. For example, a catalyst having a cylindricalshape preferably has a ratio of length to diameter (outer diameter) (L/Dratio) of 1˜1.3, and more preferably has a L/D ratio of 1. A catalysthaving a cylindrical or spherical shape preferably has an outer diameterof 3˜10mm, more preferably of 5˜8mm.

The Mo—Bi—Nb—Te based composite metal oxide according to the presentinvention may be prepared by a conventional method for producing acomposite metal oxide, except that a different composition of elementsis used.

There is no particular limitation in the shape of a metal precursorforming the Mo—Bi—Nb—Te based composite metal oxide. For example, acompound that is provided originally in the form of an oxide or can beconverted into an oxide by heating (i.e. calcination) at least in thepresence of oxygen, for example, halogenide, nitride, formate, oxalate,citrate, acetate, carbonate, amine complex, ammonium salt and/orhydroxide may be used as a starting material.

According to an embodiment of the present invention, the method forpreparing the composite metal oxide comprises the steps of: dissolvingor dispersing a predetermined amount (stoichiometric amount) of eachstarting material containing each element forming the composite metaloxide into an aqueous medium; heating the resultant solution ordispersion while stirring it; allowing the system to evaporate to obtaina dry solid and drying and pulverizing the solid; and molding the powderinto a desired shape via extrusion molding to obtain tablets orgranules. In this case, glass fibers and inorganic fibers includingvarious kinds of whiskers, which are known to improve the strength andfrictional resistance, may be further added. Additionally, in order tocontrol the properties of the catalyst and to obtain excellentreproducibility, other additives known as powder binders, such asammonium nitrate, cellulose, starch, polyvinyl alcohol, stearic acid, orthe like, may be used.

The composite metal oxide catalyst according to the present inventionmay be obtained by calcining the molded product obtained as describedabove or the same product supported on a carrier under a flow of 0.2˜2m/s at 300˜600° C. for about 1˜10 hours. The calcination step may beperformed under an inert gas atmosphere, an oxidative atmosphere, forexample, air (a mixture of inert gas and oxygen), or a reductiveatmosphere (e.g., a mixture of inert gas, oxygen and NH₃, CO and/or H₂).The calcination step may be performed for a period of several minutes toseveral hours, and the calcination period generally decreases as thetemperature increases.

(2) The Mo—Bi—Nb—Te based composite metal oxide according to the presentinvention may be used as a catalyst to produce (meth)acrylic acid fromat least one reactant selected from the group consisting of propylene,propane, isobutylene, t-butyl alcohol, and metyl-t-butyl ether. In thiscase, conversion (selectivity) from propylene or the like into(meth)acrolein and (meth)acrylic acid may be accomplished at a ratio of90% or more, and the molar ratio of (meth)acrolein:(meth)acrylic acid inthe reaction product is approximately 8:2˜7:3.

Particularly, the Mo—Bi—Nb—Te based composite metal oxide according tothe present invention may be used as a catalyst for the first-steppartial oxidation in a process for producing (meth)acrylic acid from areaction material such as propylene or the like, the process comprisinga first step for producing (meth)acrolein as a main product from thereactants such as propylene or the like and a second step for producing(meth)acrylic acid from the (meth)acrolein.

When vapor phase catalytic oxidation is carried out by using theMo—Bi—Nb—Te based composite metal oxide according to the presentinvention as a catalyst, there is no particular limitation in systemsand operation conditions thereof used in the process. Reactors that maybe used in the present invention include conventional fixed-bed,fluidized-bed and moving-bed reactors. For example, the process forproducing (meth)acrylic acid may be performed in a shell-and-tubereactor and the Mo—Bi—Nb—Te based composite metal oxide according to thepresent invention may be packed in a reaction tube so as to be used as afirst-step fixed bed catalyst. Herein, as a second-step catalyst,Mo—V-based multinary metal oxide may be used to oxidize(meth)acrolein-containing mixed product gas generated by the first-stepMo—Bi—Nb—Te based composite metal oxide catalyst, thereby producing(meth)acrylic acid.

To perform the reaction, reaction conditions, which are generallyadopted for producing (meth)acrylic acid and (meth)acrolein from areaction material such as propylene or the like via vapor phasecatalytic oxidation, may be used. For example, a gas mixture as astarting material, which contains 7 vol % or more of reactants such aspropylene or the like, 10˜13 vol % of molecular oxygen and 60˜80 vol %of inert gas functioning as a diluent (e.g. nitrogen, carbon dioxide,steam, or the like), is caused to be in contact with the catalystaccording to the present invention, at a temperature of 250˜500° C.under a pressure of 0.1˜3 kg/cm² G with a space velocity of 300˜5000hr⁻¹ (STP) to carry out a desired reaction.

The second-step catalytic reaction is suitably carried out at a reactiontemperature of 200˜450° C., preferably of 265˜370° C., under a reactionpressure of 0.1˜10 atm, preferably of 0.5˜3 atm. For example, a feed gasas reactants, which contains 4˜10 vol % of (meth)acrolein, 10˜13 vol %of oxygen, 5˜60 vol % of water steam and 20˜80 vol % of inert gas, isintroduced onto the catalyst with a space velocity of 500˜5000 hr⁻¹(STP) to perform oxidation.

(3) Further, the present invention provides a process for producing(meth)acrylic acid comprising a first step of producing (meth)acroleinas a main product from propylene or the like, and a second step ofproducing (meth)acrylic acid from the (meth)acrolein, wherein yield of(meth)acrylic acid in the product of the first step is 20 mole % orhigher.

The yield as high as 20 mol % of (meth)acrylic acid in the first-stepreaction product can be accomplished by using the Mo—Bi—Nb—Te basedcomposite metal oxide according to the present invention as thefirst-step catalyst.

Meanwhile, when (meth)acrylic acid is produced with a yield of 20 mole %or higher in the first-step reaction product, it is possible to obtain aconversion ratio of (meth)acrolein of 98˜100%, preferably 100%, in thesecond-step reaction. Herein, the (meth)acrolein conversion ratio ashigh as 98˜100% also depends on the content of propylene or the like inthe reaction mixture introduced to the first-step. Preferably, propyleneor the like is contained in the reaction mixture gas introduced into thefirst-step reaction in an amount of 7˜10 vol % in order to accomplish a(meth)acrolein conversion ratio of 100%.

MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention. It is to be understood that the following examplesand comparative examples are illustrative only, and the scope of thepresent invention is not limited thereto.

PREPARATION OF FIRST-STEP REACTION CATALYST Preparation Example 1

Catalyst 1

First, 2500 ml of distilled water was heated and stirred at 70° C.˜85°C. and 1000 g of ammonium molybdate was added thereto to form solution(1). Next, 274 g of bismuth nitrate, 228 g of ferrous nitrate and 2.3 gof potassium nitrate were added to 400 ml of distilled water, thematerials were mixed thoroughly, 71 g of nitric acid was added thereto,and the materials were dissolved sufficiently to form solution (2). To200 ml of distilled water, 686 g of cobalt nitrate was dissolved to formsolution (3). After mixing solution (2) with solution (3), the mixedsolution was further mixed with solution (1) while maintaining thetemperature at 40˜60° C. to provide a catalyst suspension.

The catalyst suspension was dried to produceMo₁₂Bi_(1.2)Fe_(1.2)Co₅K_(0.05) and the catalyst was pulverized into asize of 150 μm or less. The resultant catalyst powder was mixed for 2hours and formed into a cylindrical shape. The catalyst was formed tohave an outer diameter of 4.0˜8.0 mm, and calcined at 500° C. for 5hours under the air, and then the catalytic activity was verified.

Preparation Example 2

Catalyst 2

Catalyst 2 was provided in the same manner as described in PreparationExample 1, except that 63 g of niobium chloride and 150 g of telluriumchloride were further added to form solution (1). The catalyst had theelemental composition of Mo₁₂Nb_(0.5)Te₁Bi_(1.2)Fe_(1.2)Co₅K_(0.05)except oxygen.

Preparation Example 3

Catalyst 3

Catalyst 3 was provided in the same manner as described in PreparationExample 1, except that 127 g of niobium chloride and 150 g of telluriumnitrate were further added to form solution (1). The catalyst had theelemental composition ofMo₁₂Nb_(1.0)Te_(1.0)Bi_(1.2)Fe_(1.2)Co_(4.5)K_(0.05) except oxygen.

Preparation Example 4

Catalyst 4

Catalyst 4 was provided in the same manner as described in PreparationExample 1, except that 63 g of niobium chloride and 75 g of telluriumchloride were further added to form solution (1). The catalyst had theelemental composition of Mo₁₂Nb_(0.5)Te₁Bi_(1.2)Fe_(1.2)Co_(4.5)K_(0.05)except oxygen.

Preparation Example 5

Catalyst 5

First, 2000 ml of distilled water was heated and stirred at 100° C. and246 g of ammonium tungstate, 1000 g of ammonium molybdate and 220 g ofammonium vanadate were dissolved therein to form solution (1). Next, 228g of copper nitrate and 49 g of strontium nitrate were added to 500 mlof distilled water, and the materials were mixed thoroughly to formsolution (2). Solution (1) was mixed with solution (2) to provide asuspension. The suspension was treated by using a homogenizer for atleast 30 minutes and was coated on spherical carriers having an outerdiameter of 4.0˜8.0 mm by using a spray nozzle to an amount of 20˜30 wt% as expressed by the catalytically active component present in thesuspension. The coated catalyst was dried at 120° C. sufficiently andcalcined at 400° C. for at least 5 hours to provide spherical catalystparticles having a final outer diameter of 5 mm(±0.2).

The catalyst had the elemental composition ofMo₁₂W_(2.0)V_(4.0)Cu_(2.0)Sro_(0.5) except oxygen.

Experiment: Catalyst Packing and Catalytic Activity Test

To a 3 m stainless steel reactor having an inner diameter of 1 inch andheated with molten nitrate salt, alumina silica was packed to a heightof 150 mm as an inert material, and any one of Catalysts 1˜4 was packedto a height of 2800 mm as the first-step catalyst, from the inlet of thereaction gas toward the outlet.

Then, alumina silica was packed to a height of 150 mm as an inertmaterial and Catalyst 5 was packed to a height of 2900 mm as thesecond-step catalyst. Propylene was subjected to vapor phase oxidationby using the reactor to produce acrolein and acrylic acid. Thefirst-step oxidation was performed by introducing feed gas containing 7vol % of propylene, 13 vol % of molecular oxygen, 8 vol % of water steamand 72 vol % of inert gas onto the catalyst with a space velocity of1500 hr⁻¹ (STP), at a reaction temperature of 320° C., under a reactionpressure of 0.7 atm. The second-step oxidation was performed at areaction temperature of 276° C., under a reaction pressure of 0.1˜3kg/cm² G.

In the following Tables 1 and 2, conversion ratio of a reactionmaterial, selectivity and yield are calculated based on the followingMathematical Formulae 1˜7.first-step propylene conversion ratio(%)=[moles of reactedpropylene/moles of supplied propylene]×100  [Mathematical Formula 1]yield(%) of acrolein in the first step=[moles of produced acrolein/molesof supplied propylene]×100  [Mathematical Formula 2]yield(%) of acrylic acid in the first step=[moles of produced acrylicacid/moles of supplied propylene]×100  [Mathematical Formula 3]selectivity(%) of acrolein+acrylic acid in the first step=[moles ofproduced acrolein and acrylic acid/moles of reactedpropylene]×100  [Mathematical Formula 4]second-step acrolein conversion ratio(%)=[moles of reactedacrolein/moles of supplied acrolein]×100  [Mathematical formula 5]yield(%) of acrylic acid in the second step=[moles of produced acrylicacid/moles of supplied acrolein]×100  [Mathematical Formula 6]selectivity(%) of acrylic acid in the second step =[moles of producedacrylic acid/moles of reacted acarolein]×100  [Mathematical Formula 7]

The experimental results of the Examples according to the presentinvention and Comparative Example are shown in the following Table 1(first-step oxidation) and Table 2 (second-step oxidation).

TABLE 1 Acrylic acid + Propylene Acrylic acid acrolein conversion (%)Acrolein yield yield (*1) selectivity Item 320° C. (mole %) (mole %) (%)Comp. Ex. 1 97.01 80.21 9.31 92.27 (Catalyst 1) Ex. 1 97.21 65.34 25.5693.50 (Catalyst 2) Ex. 2 97.60 66.12 26.14 95.05 (Catalyst 3) Ex. 398.01 66.04 26.19 94.10 (Catalyst 4)

TABLE 2 Acrolein conversion (mole %) Reaction Acrylic acid Acrylic acidtemperature yield (*2) selectivity Item 276° C. (mole %) (mole %) Comp.Ex. 1 98.14 87.12 88.77 (Catalyst 1 + Catalyst 5) Ex. 1 100 90.90 90.90(Catalyst 2 + Catalyst 5) Ex. 2 100 92.26 92.26 (Catalyst 3 + Catalyst5) Ex. 3 100 92.23 92.23 (Catalyst 4 + Catalyst 5)

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing, when the Mo—Bi—Nb—Te based compositemetal oxide according to the present invention is used as the first-stepcatalyst in the production of (meth)acrylic acid from propylene or thelike, yield and/or selectivity of (meth)acrylic acid increases in thefirst-step reaction product, and thus (meth)acrolein load decreases inthe second-step to such a degree that (meth)acrolein conversion ratiocan reach 98˜100%.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiment and the drawings. On the contrary, it is intendedto cover various modifications and variations within the spirit andscope of the appended claims.

1. A process for producing (meth)acrylic acid comprising a first step ofproducing (meth)acrolein as a main product from at least one reactionmaterial selected from the group consisting of propylene, propane,isobutylene, t-butyl alcohol and methyl-t-butyl ether, and a second stepof producing (meth)acrylic acid from the (meth)acrolein, wherein yieldof (meth)acrylic acid in the product of the first step is 20 mole % orhigher.
 2. The process according to claim 1, wherein the first-stepreaction product includes (meth)acrolein and (meth)acrylic acid in amolar ratio ((meth)acrolein: (meth)acrylic acid) of 8:2˜7:3.
 3. Theprocess according to claim 1, wherein a Mo—Bi—Nb—Te based compositemetal oxide is used as the first-step catalyst.
 4. The process accordingto claim 3, wherein the Mo—Bi—Nb—Te based composite metal oxide isrepresented by the following Formula 1:MO_(a) Bi_(b) Nb_(c) Te_(d) A_(e) B_(f) C_(g) D_(h) E_(i) F_(j)O_(k)  [Formula 1] Wherein Mo represents molybdenum, Bi representsbismuth, Nb represents niobium, and Te represents tellurium; A is atleast one element selected from the group consisting of W, Sb, As, P, Snand Pb; B is at least one element selected from the group consisting ofFe, Zn, Cr, Mn, Cu, Ru, Pd, and Ag; C is at least one element selectedfrom the group consisting of Co, Cd, Ta, Pt and Ni; D is at least oneelement selected from the group consisting of Si, Al, Zr, V and Ce; E isat least one element selected from the group consisting of Se, Ga, Ti,Ge, Rh and Au; F is at least one element selected from the groupconsisting of Na, K, Li, Rb, Cs, Ca, Mg, Sr, and Ba; each of a, b, c, d,e, f, g, h, i, j and k represents the atomic ratio of each element;wherein when a=12, b is 0.01˜20, c is 0.001˜20, d is 0.001˜20, e is0˜15, f is 0˜20, g is 0˜20, h is 0˜10, i is 0˜10, j is 0˜10, and k is anumber defined by the oxidation state of each of the above elements. 5.The process according to claim 1, wherein conversion ratioof(meth)acrolein in the second step is 98%˜100%.
 6. The processaccording to claim 1, wherein the reaction material introduced into thefirst step comprises at least one reaction material selected from thegroup consisting of propylene, propane, isobutylene, t-butyl alcohol andmethyl-t-butyl ether in a concentration of 7˜10 vol %.